1. Field of the Invention
The present invention relates to a vehicle lighting device in which a light source unit including at least a light emitting device as a light source and a projection lens as a light distributing member for distributing light from the light source forward are provided in a lamp compartment. More particularly, the present invention relates to a vehicle lighting device that forms a predetermined light distribution pattern by combining light beam patterns emitted from a plurality of light source units provided in the lamp compartment.
2. Description of the Background Art
In general, as an example, a vehicle headlamp is configured to form a low beam light distribution pattern having a cut-off line along an upper edge of the pattern, whereby a forward visibility for the driver of the subject vehicle is secured as much as possible while suppressing the generation of glare to the driver of an oncoming vehicle or the like.
The following discussion refers to two background vehicle headlamps disclosed in JP-A-2005-166588 (hereinafter “Patent Document No. 1”) and JP-A-2000-100214 (hereinafter “Patent Document No. 2”).
In recent years, there has been a vigorous tendency to develop vehicle headlamps which use light emitting devices as light sources. Patent Document No. 1 discloses a vehicle headlamp in which a plurality of light source units using light emitting devices as their light sources are provided in a lamp compartment and a low beam light distribution pattern is formed by overlapping respective light beam patterns formed by the light source units so provided.
As is shown in FIG. 12, each light source unit is made up of a light distribution control member and a light emitting device 2 as a light source. The light distribution control member includes a reflector 7, a shade 6 for forming a cut-off line, and a projection lens 4. The light source unit is mounted integrally on a front side of a bracket 1, which makes up a unit support member.
Since light of the light emitting device 2 used as the light source has little heat, the projection lens 4 and the cut-off line forming shade 6 can be made from a synthetic resin with a view to reducing the weight thereof. The bracket 1, which is the unit support member on which the light emitting device 2 is mounted, can be made of a die-cast metallic product having a good heat conductive property with a view to suppressing the increase in temperature of the light emitting device 2, which could lead to the reduction in the life of the light emitting device 2. High temperatures can cause the light emitting device to eventually experience a reduction in light flux and/or change in the color of light emitted from the light emitting device 2.
An acrylic resin lens 4 and a polycarbonate resin shade 6 may be integrated into a single unit by insert molding. The resin shade 6 and the metallic bracket 1 may be fastened together with a metallic fastening screw 8. A bracket 7a of the reflector 7 and a bracket of the shade 6 may also be fastened together with the fastening screw 8.
Although it does not disclose a projection type lamp in which light is projected and distributed by a projection lens as disclosed in Patent Document No. 1, Patent Document No. 2 discloses a reflection type headlamp which forms a predetermined light distribution pattern by reflecting light from a light source by a reflector, and this reflection type headlamp has a lamp construction in which a resin outer lens that is to be assembled to a front opening in a resin housing is fixed to the resin housing by means of ultrasonic welding.
A vehicle headlamp, such as shown in Patent Document No. 1 above, in which a low beam light distribution pattern is formed by overlapping light beam patterns formed by a plurality of light source units, requires positional accuracy between the resin lens 4 and shade 6 which are the light distribution control members. Such a vehicle headlamp also requires that the positional accuracy of the light distribution control members (i.e., the lens 4 and the shade 6) relative to the bracket 1 be maintained. Namely, respective optical axes of the light source units need to be aligned. Due to this, a construction is adopted in which a plurality of positioning projections 6b are provided on an abutment surface of the shade 6 against the bracket 1 in order to secure a positional accuracy of the light distribution control members (i.e., the lens 4 and the shade 6) relative to the bracket 1.
In Patent Document No. 1, however, the resin lens 4 and resin shade 6 are integrated into the single unit by means of insert molding. As a result, a mold for integrally molding both the lens 4 and the shade 6 is complex, and large-sized molding equipment becomes necessary, resulting in an increase in production cost.
To cope with this, the inventor considered that as with Patent Document No. 2, in the event that the resin projection lens 4 and the resin shade 6 are formed into an integrated unit by welding such as ultrasonic welding, there is no need for a complex mold for integrating both the lens 4 and the shade 6 into a single unit, nor is large-sized molding equipment necessary. Therefore, the increase in production cost is suppressed.
However, in the event that the resin lens 4 and the resin shade 6 are integrated into the single unit by means of welding, burrs produced at the weld between the lens and the shade protrude (i.e., are exposed) towards an optical axis side of the lens 4, whereby the light distribution is adversely affected or the burrs become visible through the lens 4, such that the appearance of the headlamp when not lit is deteriorated.
The inventor next considered a construction in which a projection is formed on a rear surface side of the resin lens 4, while a stepped portion is formed on an outer circumference of a distal end portion of the resin shade 6 as a lens abutment portion so that the projection on the lens 4 is brought into longitudinal engagement therewith. The projection on the lens 4 and the stepped portion on the shade 6 are welded together so that the lens 4 and the shade 6 are integrated. An inner circumferential side of the stepped portion of the shade 6 functions as a barrier to prevent fused resin produced at the time of welding from flowing out towards the optical axis side of the lens 4. In other words, the fused resin does not protrude towards the optical axis side of the lens 4 to thereby avoid the protrusion of burrs. The inventor produced this construction as an experiment to study the effectiveness thereof and confirmed that the construction was effective, leading to the filing of the instant application.